The present disclosure relates generally to integrated circuits and, more specifically, to a pair of parallel diodes in the integrated circuit.
Zener or avalanche diodes are used to limit voltages seen by components in an integrated circuit. These diodes are either discrete components external to the integrated circuit or specially integrated into the integrated circuit with the elements they are to protect. Discrete diodes add to the overall costs at the component and the printed circuit board level. Integrated circuit Zener diodes add to the cost by increasing the die area.
Certain circuits parasitic have intentional inductances that lead to large voltage spikes during fast switching events. Voltage spikes frequently exceed the breakdown of the integrated circuit transistors especially, when the transistors drain to source on-resistance is being minimized. Depending upon the device's architecture, repetitive breakdown events lead to hot carrier charge be trapped. Lateral MOS transistors are particularly susceptible.
An integrated circuit of the present disclosure includes a first and second diode connected in parallel. The first diode has a first breakdown voltage and has first P type region and first N type region adjacent to each other at the surface of the substrate to form a lateral diode. The second diode has a second breakdown voltage less than the first breakdown voltage and has a second P type region and second N type region lateral adjacent to each other in the substrate to form a lateral diode below the surface. The first and second N type regions overlap and the first and second P type region are electrically connected whereby the first and second diodes are in parallel.
The second P type and N type regions have a maximum impurity concentration below the surface of the substrate. The substrate may include a lateral insulation, for example a trench in the surface, and the second diode is below the trench. The first and second P type regions may be spaced in the substrate and are electrically connected by interconnects above the substrate. The first and second P type regions may alternatively overlap to form the electrical connection. The first and second P type regions may be a common P type region abutting the first N type region at the surface and the second N type region below the surface. The common P type region and the N type region have a maximum impurity concentration below the surface of the substrate.
The first P type region may be a body of a lateral field effect transistor and the first N type region is a drain region of the field effect transistor. The field effect transistor may be an insulated gate field effect transistor.
These and other aspects of the present disclosure will become apparent from the following detailed description of the disclosure, when considered in conjunction with accompanying drawings.